There are some dependencies that exist between the various infrastructure
elements that get created in the cloud. While this is necessary in order to
have things work correctly, it does cause the occasional problem when trying to
delete unwanted items.

If you are looking to only remove certain elements, then you would have to
ensure that all dependencies on that network are removed first. In some
cases, these dependencies might be nested, meaning that the obvious
dependency may also have less obvious dependencies.

One example of this would be trying to remove a network that is connected
to a router but also still in use by a VPN. If you try and remove the router
interface through the dashboard, you would get a non-specific error indicating
that removing the interface failed.

At this point it may be quite challenging to determine what the exact cause
of the error is. The best way to diagnose the problem is to use the OpenStack
command line tools.

Success: now you can see what the problem is. It appears that your subnet is
associated with a VPN. If you were to go ahead and remove the VPN, you would
be able to delete the network as you initially set out to do.